The most formidable cases brought forward by Mr. Spencer are from Darwin. I shall endeavour to show, however, that Darwin was probably wrong in retaining the older explanation of these facts, and that the remains of the Lamarckian theory of use-inheritance need not any longer encumber the great explanation which has superseded that fallacious and unproven theory and has rendered it totally unnecessary. Meanwhile I think it is an excellent sign that Mr. Spencer has to complain that "Nowadays most naturalists are more Darwinian than Mr. Darwin himself"—inasmuch as they are inclined to say that there is "no proof" that the effects of use and disuse are inherited. Other excellent signs are the recent issue of a translation of Weismann's important essays on this and kindred subjects,[15] the strong support given to his views by Wallace in his Darwinism, and their adoption by Ray Lankester in his article on Zoology in the latest edition of the EncyclopÆdia Britannica. So sound and cautious an investigator as Francis Galton had also in 1875 concluded that "acquired modifications are barely, if at all, inherited, in the correct sense of that word."

Darwin's belief in the inheritance of acquired characters was more or less hereditary in the family. His grandfather, Erasmus Darwin, anticipated Lamarck's views in his Zoonomia, which Darwin at one time "greatly admired." His father was "convinced" of the "inherited evil effects of alcohol," and to this extent at least he strongly impressed the belief in the inheritance of acquired characters upon his children's minds.[16] Darwin must also have been imbued with Lamarckian ideas from other sources, although Dr. Grant's enthusiastic advocacy entirely failed to convert him to a belief in evolution.[17] "Nevertheless," he says, "it is probable that the hearing rather early in life such views maintained and praised may have favoured my upholding them under a different form in my Origin of Species"—a remark which refers to Lamarck's views on the general doctrine of evolution, but might also prove equally true if applied to Darwin's partial retention of the Lamarckian explanation of that evolution. Professor Huxley has pointed out that in Darwin's earlier sketch of his theory of evolution (1844) he attached more weight to the inheritance of acquired habits than he does in his Origin of Species published fifteen years later.[18] He appears to have acquired the belief in early life without first questioning and rigorously testing it as he would have done had it originated with himself. In later life it appeared to assist his theory of evolution in minor points, and in particular it appeared absolutely indispensable to him as the only explanation of the diminution of disused parts in cases where, as in domestic animals, economy of growth seemed to be practically powerless. He failed to adequately notice the effect of panmixia, or the withdrawal of selection, in causing or allowing degeneracy and dwindling under disuse; and he hardly attached sufficient importance to the fact that rudimentary organs and other supposed effects of use or disuse are quite as marked features in neuter insects which cannot transmit the effects of use and disuse as they are in the higher animals.

REDUCED WINGS OF BIRDS OF OCEANIC ISLANDS.

Darwin himself has pointed out that the rudimentary wings of island beetles, at first thought to be due to disuse, are mainly brought about by natural selection—the best-winged beetles being most liable to be blown out to sea. But he says that in birds of the oceanic islands "not persecuted by any enemies, the reduction of their wings has probably been caused by disuse." This explanation may be as fallacious as it is acknowledged to have been in the case of the island beetles. According to Darwin's own views, natural selection must at least have played an important part in reducing the wings; for he holds that "natural selection is continually trying to economize every part of the organization." He says: "If under changed conditions of life a structure, before useful, becomes less useful, its diminution will be favoured, for it will profit the individual not to have its nutriment wasted in building up an useless structure.... Thus, as I believe, natural selection will tend in the long run to reduce any part of the organization, as soon as it becomes, through changed habits, superfluous."[19] If, as Darwin powerfully urges (and he here ignores his usual explanation), ostriches' wings are insufficient for flight in consequence of the economy enforced by natural selection,[20] why may not the reduced wings of the dodo, or the penguin, or the apteryx, or of the Cursores generally, be wholly attributed to natural selection in favour of economy of material and adaptation of parts to changed conditions? The great principle of economy is continually at work shaping organisms, as sculptors shape statues, by removing the superfluous parts; and a mere glance at the forms of animals in general will show that it is well-nigh as dominant and universal a principle as is that of the positive development of useful parts. Other causes, moreover besides actual economy, would favour shorter and more convenient wings on oceanic islands. In the first place, birds that were somewhat weak on the wing would be most likely to settle on an island and stay there. Shortened wings would then become advantageous because they would restrain fatal migratory tendencies or useless and perilous flights in which the birds that flew furthest would be most often carried away by storms and adverse winds. Reduced wings would keep the birds near the shelter and the food afforded by the island and its neighbourhood, and in some cases would become adapted to act as fins or flappers for swimming under water in pursuit of fish.

The reduced size of the wings of these island birds is paralleled by the remarkable thinness, &c., of the shell of the "gigantic land-tortoise" of the Galapagos Islands. The changes seen in the carapace can hardly have been brought about by the inherited effects of special disuse. Why then should not the reduction of equally useless, more wasteful, and perhaps positively dangerous wings be also due to an economy which has become advantageous to bird and reptile alike through the absence of the mammalian rivals whose places they are evidently being modified to fill? The complete loss of the wings in neuter ants and termites can scarcely be due to the inherited effects of disuse; and as natural selection has abolished these wings in spite of the opposition of use-inheritance, it must clearly be fully competent to reduce wings without its aid. In considering the rudimentary wings of the apteryx, or of the moa, emu, ostrich, &c., we must not forget the frequent or occasional occurrence of hard seasons, and times of drought and famine, when Nature eliminates redundant, wasteful, and ill-adapted organisms in so severe and wholesale a fashion. Where enemies are absent there would be unrestrained multiplication, and this would greatly increase the severity of the competition for food, and so hasten the elimination of disused and useless parts.

DROOPING EARS AND DETERIORATED INSTINCTS.

Mr. Galton has pointed out that existing races and existing organs are only kept at their present high pitch of organic excellence by the stringent and incessant action of natural or artificial selection; and the simple relaxation or withdrawal of such selective influences will almost necessarily result in a certain amount of deterioration, independently even of the principle of economy.[21] I think that this cessation of a previous selective process will account for the drooping—but not diminished—ears of various domesticated animals (human preference and increased weight evidently aiding), and also for the inferior instincts seen in them and in artificially-fed caterpillars of the silk-moth, which now "often commit the strange mistake of devouring the base of the leaf on which they are feeding, and consequently fall down." Anyhow, I fail to see that anything is proved by this latter case, except that natural instinct may be perverted or aborted under unnatural conditions and a changed method of selection which abolishes the powerful corrective formerly supplied by natural selection.

WINGS AND LEGS OF DUCKS AND FOWLS.

The reduced wings and enlarged legs of domesticated ducks and fowls are attributed by Darwin and Spencer to the inheritance of the effects of use and disuse. But the inference by no means follows. Natural selection would usually favour these adaptive changes, and they would also have been aided by an artificial selection which is often unconscious or indirect. Birds with diminished power of flight would be less difficult to keep and manage, and in preserving and multiplying such birds man would be unconsciously bringing about structural changes which would easily be regarded as effects of use and disuse. "About eighteen centuries ago Columella and Varro speak of the necessity of keeping ducks in netted enclosures like other wild fowl, so that at this period there was danger of their flying away."[22] Is it not probable that the best fliers would escape most frequently, or would pine most if kept confined? On the other hand, birds with lessened powers of flight would not be eliminated as under natural conditions, but would be favoured; and natural selection, together with artificial selection of the most flourishing birds, would thicken and strengthen the legs to meet increased demands upon them.

The diminution of the duck's wing is not great even in the birds that "never fly," and from this we must deduct the direct effect of disuse on the individual during its lifetime. As Weismann suggests, the inherited portion of the change could only be ascertained by comparing the bones, &c., of wild and tame ducks similarly reared. If individual disuse diminished the weight of the duck's wing-bones by 9 per cent. there would be nothing left to account for.

I suspect that investigation would reveal anomalies inconsistent with the theory of use-inheritance. Thus according to Darwin's tables of comparative weights and measurements[23] the leg-bones of the Penguin duck have slightly diminished in length, although they have increased 39 per cent. in weight. Relatively to the weight of the skeleton, the leg-bones have shortened in the tame breeds of ducks by over 5 per cent. (and in two breeds by over 8 per cent.) although they have increased more than 28 per cent. in proportional weight.[24] How can increased use simultaneously shorten and thicken these bones? If the relative shortening is attributed to a heavier skeleton, then the apparently reduced weight of the wing-bones is fully accounted for by the same circumstance, and disuse has had no inherited effect.

Another strange circumstance is that the wing-bones have diminished in length only. The shortening is about 6 per cent. more than in the shortened legs, and it amounts to 11 per cent. as compared with the weight of the skeleton. Such a shortening should represent a reduction of 29 per cent. in weight, whereas the actual reduction in the weight of the wing-bones relatively to the weight of the skeleton is only 9 per cent. even in the breeds that never fly. Independently of shortening, the disused wing-bones have actually thickened or increased in weight. In the Aylesbury duck the disproportion caused by these conflicting changes is so great that the wing-bones are 47 per cent. heavier than they should be if their weight had varied proportionally with their length.[25] The reduction in weight on which Darwin relies seems to be entirely due to the shortening, and this shortening appears to be irrelevant to disuse, since the wings of the Call duck are similarly shortened in their proportions by 12 per cent., although this bird habitually flies to such an extent that Darwin partly attributes the greatly increased weight of its wing-bones to increased use under domestication.

We find that all the changes are in the direction of shorter and thicker bones—a tendency which must be largely dependent upon the suspension of the rigorous elimination which keeps the bones of the wild duck long and light. The used leg-bones and the disused wing-bones have alike been shortened and thickened, though in different proportions. Natural or artificial selection might easily thicken legs without lengthening them, or shorten wings without eliminating strong heavy bones, but it can hardly be contended that use-inheritance has acted in such conflicting ways. The thickening of the wing-bones has actually more than kept pace with any increase of weight in the skeleton, in spite of the effect of individual disuse and of the alleged cumulative effect of ancestral disuse for hundreds of generations. The case of the duck deserves special attention as a crucial one, if only from the fact that in this instance, and in this instance only, has Darwin given the weights of the skeletons, thus furnishing the means for a closer examination of his details than is usually possible.

If we ignore such factors as selection, panmixia, correlation, and the effects of use and disuse during lifetime, and still regard the case of the domestic duck as a valid proof of the inheritance of the effects of use and disuse, we must also accept it as an equally valid proof that the effects of use and disuse are not inherited. Nay, we may even have to admit that, in two points out of four, the inherited effect of use and disuse on successive generations is exactly opposite to the immediate effect on the individual.

Among fowls the wing-bones have lost much in weight but little or nothing in length—which is the reverse of what has occurred in ducks, although disuse is alleged to be the common cause in both cases. Some of the fowls which fly least have their wing-bones as long as ever. In the case of the Silk and Frizzled fowls—ancient breeds which "cannot fly at all"—and in that of the Cochins, which "can hardly fly up to a low perch," Darwin observes "how truly the proportions of an organ may be inherited although not fully exercised during many generations."[26] In four out of twelve breeds the wing-bones had become slightly heavier relatively to the leg-bones. Do not these facts tend to show that the changes in fowls' wings are due to fluctuating variability and selective influences rather than to a general law whereby the effects of disuse are cumulatively inherited?

PIGEONS' WINGS.

Concerning pigeons' wings Darwin says: "As fancy pigeons are generally confined in aviaries of moderate size, and as even when not confined they do not search for their own food, they must during many generations have used their wings incomparably less than the wild rock-pigeon ... but when we turn to the wings we find what at first appears a wholly different and unexpected result."[27] This unexpected increase in the spread of the wings from tip to tip is due to the feathers, which have lengthened in spite of disuse. Excluding the feathers, the wings were shorter in seventeen instances, and longer in eight. But as artificial selection has lengthened the wings in some instances, why may it not have shortened them in others? Wings with shortened bones would fold up more neatly than the long wings of the Carrier pigeon for instance, and so might unconsciously be favoured by fanciers. The selection of elegant birds with longer necks or bodies would cause a relative reduction in the wings—as with the Pouter, where the wings have been greatly lengthened but not so much as the body.[28] Slender bodies, too, and the lessened divergence of the furculum,[29] would slightly diminish the spread of the wings, and so would affect the measurements taken. As the wing-bones, moreover, are to some extent correlated with the beak and the feet, the artificial selection of shortened beaks might tend to shorten the wing as well as the feet. Under these circumstances how can we be sure of the actual efficacy of use-inheritance? Surely selection is as fully competent to effect slight changes in the direction of use-inheritance as it undoubtedly is to effect great changes in direct opposition to that alleged factor of evolution.

SHORTENED BREAST-BONE IN PIGEONS.

The shortening of the sternum in pigeons is attributed to disuse of the flight muscles attached to it. The bone is only shortened by a third of an inch, but this represents a very remarkable reduction in proportional length, which Darwin estimates at from one-seventh to one-eighth, or over 13 per cent. This marked reduction, too, quite unlike the slight reduction of the wing-bones to which the other ends of the muscles are attached, was universal in the eleven specimens measured by Darwin; and the bone, though acknowledged to have been modified by artificial selection in some breeds, is not so open to observation as wings or legs. Even, however, if this relative shortening of the sternum remained otherwise inexplicable, it might still be as irrelevant to use and disuse as is the fact that "many breeds" of fancy pigeons have lost a rib, having only seven where the ancestral rock-pigeon has eight.[30] But the excessive reduction in the sternum is far from being inexplicable. In the first place Darwin has somewhat over-estimated it. Instead of comparing the deficiency of length with the increased length which should have been acquired (since the pigeons have increased in average size) he compares it with the length of the breast-bone in the rock-pigeon.[31] By this method if a pigeon had doubled in dimensions while its breast-bone remained unaltered, the reduction would be put down as 100 per cent., whereas obviously the true reduction would be one-half, or 50 per cent. of what the bone should be. Avoiding this error and a minor fallacy besides, a sound estimate reduces the supposed reduction of 13 or 14 per cent. to one of 11·7 per cent., which is still of course a considerable diminution.

Part of this reduction must be due to the direct effect of disuse during the lifetime of the individual. Another and perhaps very considerable part of the relative change must be attributed to the lengthening of the neck or body by artificial selection, or to other modifications of shape and proportion effected directly or indirectly by the same cause.[32] The reduction is greatest in the Pouter (18½ per cent.) and in the Pied Scanderoon (17½ per cent.). In the former the body has been greatly elongated by artificial selection and three or four additional vertebrÆ have been acquired in the hinder part of the body.[33] In the latter a long neck increases the length of the bird, and so causes, or helps to cause, the relative shortening of the breast-bone. In the English Carrier—which experiences the effects of disuse, as it is too valuable to be flown—the relative reduction of 11 per cent. is apparently more than accounted for by the "elongated neck." The Dragon also has a long neck. In the Pouter, although the breast-bone has been shortened by 18½ per cent. relatively to the length of the body, it has lengthened by 20 per cent. relatively to the bulk of the body.[34] Darwin forgot to ask whether allowance must not be made for a frequent, or perhaps general, elongation of the neck and the hinder part of the body, and the relative shortening or the throwing forward of the central portion containing the ribs (frequently one less in number) and the sternum. The whole body of the pigeon is so much under the control of artificial selection, that every precaution must be taken to guard against such possible sources of error.[35]

Under domestication there would be a suspension of the previous elimination of reduced breast-bones by natural selection (Weismann's panmixia), and a diminution of the parts concerned in flying might even be favoured, as lessened powers of continuous flight would prevent pigeons from straying too far, and would fit them for domestication or confinement. Such causes might reduce some of the less observed parts affected by flying, while still leaving the wing of full size for occasional flight, or to suit the requirements of the pigeon-fanciers. A change might thus be commenced like that seen in the rudimentary keel of the sternum in the owl-parrot of New Zealand, which has lost the power of flight although still retaining fairly-developed wings.

SHORTENED FEET IN PIGEONS.

Darwin thinks it highly probable that the short feet of most breeds of pigeons are due to lessened use, though he owns that the effects of correlation with the shortened beak are more plainly shown than the effects of disuse.[36] But why need the inherited effects of disuse be called in to explain an average reduction of some 5 per cent., when Darwin's measurements show that in the breeds where long beaks are favoured the principle of correlation between these parts has lengthened the foot by 13 per cent. in spite of disuse?

SHORTENED LEGS OF RABBITS.

In the case of the domestic rabbit Darwin notices that the bones of the legs have (relatively) become shorter by an inch and a half. But as the leg-bones have not diminished in relative weight,[37] they must clearly have grown thicker or denser. If disuse has shortened them, as Darwin supposes, why has it also thickened them? The ears and the tail have been lengthened in spite of disuse. Why then may not the ungainly hind-legs have been shortened by human preference independently of the inherited effects of disuse? By relying on apparently favourable instances and neglecting the others it would be easy to arrive at all manner of unsound conclusions. We might thus become convinced that vessels tend to sail northwards, or that a pendulum oscillates more often in one direction than in the other. It must not be forgotten that it would be easy to cite an enormous number of cases which are in direct conflict with the supposed law of use-inheritance.

BLIND CAVE-ANIMALS.

Weak or defective eyesight is by no means rare as a spontaneous variation in animals, "the great French veterinary Huzard going so far as to say that a blind race [of horses] could soon be formed." Natural selection evolves blind races whenever eyes are useless or disadvantageous, as with parasites. This may apparently be done independently of the effects of disuse, for certain neuter ants have eyes which are reduced to a more or less rudimentary condition, and neuter termites are blind as well as wingless. In one species of ant (Eciton vastator) the sockets have disappeared as well as the eyes. In deep caves not only would natural selection cease to maintain good eyesight but it would persistently favour blindness—or the entire removal of the eye when greatly exposed, as in the cave-crab—and as Dr. Ray Lankester has indicated,[38] there would have been a previous selection of animals which through spontaneous weakness, sensitiveness, or other affection of the eye found refuge and preservation in the cave, and a subsequent selection of the descendants whose fitness for relative darkness led them deeper into the cave or prevented them from straying back to the light with its various dangers and severer competition. Panmixia, however, as Weismann has shown, would probably be the most important factor in causing blindness.

INHERITED HABITS.

Darwin says: "A horse is trained to certain paces, and the colt inherits similar consensual movements."[39] But selection of the constitutional tendency to these paces, and imitation of the mother by the colt, may have been the real causes. The evidence, to be satisfactory, should show that such influences were excluded. Men acquire proficiency in swimming, waltzing, walking, smoking, languages, handicrafts, religious beliefs, &c., but the children only appear to inherit the innate abilities or constitutional proclivities of their parents. Even the songs of birds, including their call-notes, are no more inherited than is language by man (Descent of Man, p. 86). They are learned from the parent. Nestlings which acquire the song of a distinct species, "teach and transmit their new song to their offspring." If use-inheritance has not fixed the song of birds, why should we suppose that in a single generation it has transmitted a newly-taught method of walking or trotting?

It is alleged that dogs inherit the intelligence acquired by association with man, and that retrievers inherit the effects of their training.[40] But selection and imitation are so potent that the additional hypothesis of use-inheritance seems perfectly superfluous. Where intelligence is not highly valued and carefully promoted by selection, the intelligence derivable from association with man does not appear to be inherited. Lap-dogs, for instance, are often remarkably stupid.

Darwin also instances the inheritance of dexterity in seal-catching as a case of use-inheritance.[41] But this is amply explained by the ordinary law of heredity. All that is needed is that the son shall inherit the suitable faculties which the father inherited before him.

TAMENESS OF RABBITS.

Darwin holds that in some cases selection alone has modified the instincts and dispositions of domesticated animals, but that in most cases selection and the inheritance of acquired habits have concurred in effecting the change. "On the other hand," he says, "habit alone in some cases has sufficed; hardly any animal is more difficult to tame than the young of the wild rabbit; scarcely any animal is tamer than the young of the tame rabbit; but I can hardly suppose that domestic rabbits have often been selected for tameness alone; so that we must attribute at least the greater part of the inherited change from extreme wildness to extreme tameness to habit and long-continued close confinement."[42]

But there are strong, and to me irresistible, arguments to the contrary. I think that the following considerations will show that the greater part, if not the whole, of the change must be attributed to selection rather than to the direct inheritance of acquired habit.

(1) For a period which may cover thousands of generations, there has been an entire cessation of the natural selection which maintains the wildness (or excessive fear, caution, activity, &c.) so indispensably essential for preserving defenceless wild rabbits of all ages from the many enemies that prey upon them.

(2) During this same extensive period of time man has usually killed off the wildest and bred from the tamest and most manageable. To some extent he has done this consciously. "It is very conducive to successful breeding to keep only such as are quiet and tractable," says an authority on rabbits,[43] and he enjoins the selection of the handsomest and best-tempered does to serve as breeders. To a still greater extent man has favoured tameness unconsciously and indirectly. He has systematically selected the largest and most prolific animals, and has thus doubled the size and the fertility of the domestic rabbit. In consciously selecting the largest and most flourishing individuals and the best and most prolific mothers, he must have unconsciously selected those rabbits whose relative tameness or placidity of disposition rendered it possible for them to flourish and to produce and rear large and thriving families, instead of fretting and pining as the wilder captives would do. When we consider how exceedingly delicate and easily disturbed yet all-important a function is that of maternity in the continually breeding rabbit, we see that the tamest and the least terrified would be the most successful mothers, and so would continually be selected, although man cared nothing for the tameness in itself. The tamest mothers would also be less liable to neglect or devour their offspring, as rabbits commonly do when their young are handled too soon, or even when merely frightened by mice, &c., or disturbed by changed surroundings.

(3) We must remember the extraordinary fecundity of the rabbit and the excessive amount of elimination that consequently takes place either naturally or artificially. Where nature preserved only the wildest, man has preserved the tamest. If there is any truth in the Darwinian theory, this thorough and long-continued reversal of the selective process must have had a powerful effect. Why should it not be amply sufficient to account for the tameness and mental degeneracy of the rabbit without the aid of a factor which can readily be shown to be far weaker in its normal action than either natural or artificial selection? Why may not the tameness of the rabbit be transferred to the group of cases in which Darwin holds that "habit has done nothing," and selection has done all?

(4) If use-inheritance has tamed the rabbit, why are the bucks still so mischievous and unruly? Why is the Angora breed the only one in which the males show no desire to destroy the young? Why, too, should use-inheritance be so much more powerful in the rabbit than with other animals which are far more easily tamed in the first instance? Wild young rabbits when domesticated "remain unconquerably wild," and, although they may be kept alive, they pine and "rarely come to any good." Yet the animal which acquires least tameness—or apparently, indeed, none at all—inherits most! It appears, in fact, to inherit that which it cannot acquire—a circumstance which indicates the selection of spontaneous variations rather than the inheritance of changed habits. Such variations occasionally occur in animals in a marked degree. Of a litter of wolf-cubs, all brought up in the same way, "one became tame and gentle like a dog, while the others preserved their natural savagery." Is it not probable that permanent domestication was rendered possible by the inevitable selection of spontaneous variations in this direction? The excessive tameness, too, of the young rabbit, while easily explicable as a result of unconscious selection, is not easily explained as a result of acquired habit. No particular care is taken to tame or teach or domesticate rabbits. They are bred for food, or for profit or appearance, and they are left to themselves most of their time. As Sir J. Sebright notices with some surprise, the domestic rabbit "is not often visited, and seldom handled, and yet it is always tame."

MODIFICATIONS OBVIOUSLY ATTRIBUTABLE TO SELECTION.

Innumerable modifications in accordance with altered use or disuse, such as the enlarged udders of cows and goats, and the diminished lungs and livers in highly bred animals that take little exercise, can be readily and fully explained as depending on selection. As the fittest for the natural or artificial requirements will be favoured, natural or artificial selection may easily enlarge organs that are increasingly used and economize in those that are less needed. I therefore see no necessity whatever for calling in the aid of use-inheritance as Darwin does, to account for enlarged udders, or diminished lungs, or the thick arms and thin legs of canoe Indians, or the enlarged chests of mountaineers, or the diminished eyes of moles, or the lost feet of certain beetles, or the reduced wings of logger-headed ducks, or the prehensile tails of monkeys, or the displaced eyes of soles, or the altered number of teeth in plaice, or the increased fertility of domesticated animals, or the shortened legs and snouts of pigs, or the shortened intestines of tame rabbits, or the lengthened intestines of domestic cats, &c.[44] Changed habits and the requisite change of structure will usually be favoured by natural selection; for habit, as Darwin says, "almost implies that some benefit great or small is thus derived."

SIMILAR EFFECTS OF NATURAL SELECTION AND USE-INHERITANCE.

Here we perceive a difficulty which will equally trouble those who affirm use-inheritance and those who deny. Broadly speaking, the adaptive effects ascribed to use-inheritance coincide with the effects of natural selection. The individual adaptability (as shown in the thickening of skin, fur, muscle, &c., under the stimulus of friction, cold, use, &c.) is identical in kind and direction with the racial adaptability under natural selection. Consequently the alleged inheritance of the advantageous effects of use and disuse cannot readily be distinguished from the similarly beneficial effects of natural selection. The indisputable fact that natural selection imitates or simulates the beneficial effects ascribed to use-inheritance may be the chief source and explanation of a belief which may prove to be thoroughly fallacious. A similar simulation of course occurs under domestication, where natural selection is partly replaced by artificial selection of the best adapted and therefore most flourishing animals, while in disused parts panmixia or the comparative cessation of selection will aid or replace "economy of growth" in causing diminution.[45]

INFERIORITY OF SENSES IN EUROPEANS.

"The inferiority of Europeans, in comparison with savages, in eyesight and in the other senses," is attributed to "the accumulated and transmitted effect of lessened use during many generations."[46] But why may we not attribute it to the slackened and diverted action of the natural selection which keeps the senses so keen in some savage races?

SHORT-SIGHT IN WATCHMAKERS AND ENGRAVERS.

Darwin notices that watchmakers and engravers are liable to be short-sighted, and that short-sight and long-sight certainly tend to be inherited.[47] But we must be careful not to beg the question at issue by assuming that the frequent heredity of short sight necessarily covers the heredity of artificially-produced short-sight. Elsewhere, however, Darwin states more decisively that "there is ground for believing that it may often originate in causes acting on the individual affected, and may thence-forward become transmissible."[48] This impression may arise (1) from the facts of ordinary heredity—the ancestral liability being excited in father and son by similar artificial habits, such as reading, and viewing objects closely as among watchmakers and engravers—or by constitutional deterioration from indoor life, &c., acting upon a constitutional liability of the eye to the "something like inflammation of the coats, under which they yield" and so cause shortness of sight by altering the spherical shape of the eye-ball. (2) Panmixia, or the suspension of natural selection, together with altered habits, will account for an increase of short-sight among the population generally. (3) Long-sighted people could not work at watchmaking and engraving so comfortably and advantageously as at other occupations, and hence would be less likely to take to such callings.

LARGER HANDS OF LABOURERS' INFANTS.[49]

These are best explained as the result of natural selection and of the diminution of the hand by sexual selection in the gentry. If the larger hands of labourers' infants are really due to the inherited effects of ancestral use, why does the development occur so early in life, instead of only at a corresponding period, as is the rule? During the first few years of its life, at least, the labourer's infant does no more work than the gentleman's child. Why are not the effects of this disuse inherited by the labourer's infant? If the enlargement of the infant's hand illustrates the transference of a character gained later in life, it is evident that the transference must take place in spite of the inherited effects of disuse.

THICKENED SOLE IN INFANTS.

Darwin also attributes the thickened sole in infants, "long before birth," to "the inherited effects of pressure during a long series of generations."[50] But disuse should make the infant's sole thin, and it is this thinness that should be inherited. If we suppose the inheritance of the thickened soles of later life to be transferred to an earlier period, we have the anomaly of the inherited effects of disuse at that earlier period being overpowered by the untimely inheritance of the effects of use at another. On the other hand, it is clear that natural selection would favour thickened soles for walking on, and might also promote an early development which would ensure their being ready in good time for actual use; for variations in the direction of delay would be cut off, while variations in the other direction would be preserved. Anyhow, the mere transference of a character to an earlier period is no proof of use-inheritance. The real question is whether the thickened sole was gained by natural selection or by the inherited effects of pressure, and the mere transference or hastened appearance of the thickening does not in any degree solve this question. It merely excludes the effect of disuse during lifetime, and thus presents a fallacious appearance of being decisive. The thickened sole of the unborn infant, however, like the lanugo or hairy covering, is probably a result of the direct inheritance of ancestral stages of evolution, of which the embryo presents a condensed epitome. While the relative thinness of the infant's sole might be pointed to as the effect of disuse during a long series of generations, its thickness is rather an illustration of atavism still resisting the effects of long-continued disuse. There is nothing to show that the inheritable portion of the full original thickness was not gained by natural selection rather than by the directly inherited effect of use; and the latter, being cumulative and indiscriminative in its action, would apparently have made the sole very much thicker and harder than it is. If natural selection were not supreme in such cases, how could we account for the effects of pressure resulting in hard hoofs in some cases and only soft pads in others?

A SOURCE OF MENTAL CONFUSION.

Of course in a certain sense this thickening of the sole has resulted from use. In one sense or other, most—or perhaps all—of the results of natural selection are inherited effects of use or disuse. Natural selection preserves that which is of use and which is used, while it eliminates that which is useless and is not used. The most confident assertions of the effects of use and disuse in modifying the heritable type, appear to rest on this indefeasible basis. Darwin's statements concerning the effects of use and disuse in evolution can frequently be read in two senses. They often command assent as undeniable truisms as they stand, but are of course written in another and more debatable sense. Thus in the case of the shortened wings and thickened legs of the domestic duck, I believe equally with Darwin and Spencer that "no one will dispute that they have resulted from the lessened use of the wings and the increased use of the legs." "Use" is at bottom the determining circumstance in evolution generally. The trunk of the elephant, the fin of the fish, the wing of the bird, the cunning hand of man and his complicated brain—and, in short, all organs and faculties whatsoever—can only have been moulded and developed by use—by usefulness and by using—but not necessarily by use-inheritance, not necessarily by directly inherited effects of use or disuse of parts in the individual. So, too, reduced or rudimentary organs are due to disuse, but it by no means follows that the diminution is caused by any direct tendency to the inheritance of the effects of disuse in the individual. The effects of natural selection are commonly expressible as effects of use and disuse, just as adaptation in nature is expressible in the language of teleology. But use-inheritance is no more proven by one of these necessary coincidences than special design is by the other. The inevitable simulation of use-inheritance may be entirely deceptive.

Darwin thinks that "there can be no doubt that use in our domestic animals has strengthened and enlarged certain parts, and disuse diminished them; and that such modifications are inherited." Undoubtedly "such" or similar modifications have often been inherited, but how can Darwin possibly tell that they are not due to the simulation of use-inheritance by natural or artificial selection acting upon general variability? Of the inevitability of selection and of its generally adaptive tendencies "there can be no doubt," and panmixia would tend to reduce disused parts; so that there must always remain grave doubts of the alleged inheritance of the similar effects of use and disuse, unless we can accomplish the extremely difficult feat of excluding both natural and artificial selection as causes of enlargement, and panmixia and selection as causes of dwindling.

WEAKNESS OF USE-INHERITANCE.

Use-inheritance is normally so weak that it appears to be quite helpless when opposed to any other factor of evolution. Natural selection evolves and maintains the instincts of ants and termites in spite of use-inheritance to a more wonderful degree than it evolves the instincts of almost any other animal with the fullest help of use-inheritance. It develops seldom-used horns or natural armour just as readily as constantly-used hoofs or teeth. Sexual selection evolves elaborate structures like the peacock's tail in spite of disuse and natural selection combined. Artificial selection appears to enlarge or diminish used parts or disused parts with equal facility. The assistance of use-inheritance seems to be as unnecessary as its opposition is ineffective.

The alleged inheritance of the effects of use and disuse in our domestic animals must be very slow and slight.[51] Darwin tells us that "there is no good evidence that this ever follows in the course of a single generation." "Several generations must be subjected to changed habits for any appreciable result."[52] What does this mean? One of two things. Either the tendency is very weak, or it is non-existent. If it is so weak that we cannot detect its alleged effects till several generations have elapsed, during which time the more powerful agency of selection has been at work, how are we to distinguish the effects of the minor factor from that of the major? Are we to conclude that use-inheritance plus selection will modify races, just as Voltaire firmly held that incantations, together with sufficient arsenic, would destroy flocks of sheep? Is it not a significant fact that the alleged instances of use-inheritance so often prove to be self-conflicting in their details?

For satisfactory proof of the prevalence of a law of use-inheritance we require normal instances where selection is clearly inadequate to produce the change, or where it is scarcely allowed time or opportunity to act, as in the immediate offspring of the modified individual. Of the first kind of cases there seems to be a plentiful lack. Of the latter kind, according to Darwin, there appears to be none—a circumstance which contrasts strangely and suspiciously with the many decisive cases in which variation from unknown causes has been inherited most strikingly in the immediate offspring. It must be expected, indeed, that among these innumerable cases some will accidentally mimic the alleged effects of use-inheritance.

If Darwin had felt certain that the effects of habit or use tended in any marked degree to be conveyed directly and cumulatively to succeeding generations, he could hardly have given us such cautious, half-hearted encouragement of good habits as the following:—"It is not improbable that after long practice virtuous tendencies may be inherited." "Habits, moreover followed during many generations probably tend to be inherited."[53] This is probable, independently of use-inheritance. The "many generations" specified or implied, will allow time for the play of selective as well as of cumulatively-educative influences. There must apparently be a constitutional or inheritable predisposition or fitness for the habits spoken of, which otherwise would scarcely be continued for many generations, except by the favourably-varying branches of a family: which again is selection rather than use-inheritance.

Where is the necessity for even the remains of the Lamarckian doctrine of inherited habit? Seeing how powerful the general principle of selection has shown itself in cases where use-inheritance could have given no aid or must even have offered its most strenuous opposition, why should it not equally be able to develop used organs or repress disused organs or faculties without the assistance of a relatively weak ally? Selection evolved the remarkable protective coverings of the armadillo, turtle, crocodile, porcupine, hedgehog, &c.; it formed alike the rose and its thorn, the nut and its shell; it developed the peacock's tail and the deer's antlers, the protective mimicry of various insects and butterflies, and the wonderful instincts of the white ants; it gave the serpent its deadly poison and the violet its grateful odour; it painted the gorgeous plumage of the Impeyan pheasant and the beautiful colours and decorations of countless birds and insects and flowers. These, and a thousand other achievements, it has evidently accomplished without the help of use-inheritance. Why should it be thought incapable of reducing a pigeon's wing or enlarging a duck's leg? Why should it be credited with the help of an officious ally in effecting comparatively slight changes, when great and striking modifications are effected without any such aid?

[15] Weismann's Essays on Heredity, &c. Clarendon Press, 1889.